Vertical furnace for processing substrates and a liner for use therein

ABSTRACT

The disclosure relates to a vertical furnace for processing a plurality of substrates and a liner for use therein. The vertical furnace having an outer reaction tube having a central axis; and a liner constructed to extend in the interior of the outer reaction tube. The liner defines an interior space for accommodating substrates and is provided with a gas exhaust hole extending from the interior space to the outside. One of the outer wall of the liner and the inner wall of the reaction tube is provided with a flow deflector that protrudes radially from the respective wall into a gas passage between an outer wall of the liner and an inner wall of the reaction tube.

FIELD

The present disclosure generally relates to equipment for processingsemiconductor substrates, and more particularly to a vertical furnaceand a liner for use therein.

BACKGROUND

Vertical processing furnaces or reactors are commonly used for batchprocessing semiconductor wafers during several fabrication stages ofintegrated circuits. Processing steps for which a furnace may be usedinclude oxidation, diffusion, annealing, chemical vapor deposition (CVD)and atomic layer deposition (ALD).

A vertical processing furnace may include a thermally resistive heatingcoil, powered by an electrical power supply. Within the heating coilthere may be provided an outer reaction tube which may be belljar-shaped and an inner reaction tube that may be substantiallycoaxially disposed within the outer reaction tube. The inner reactiontube may be commonly referred to as a liner. The lower end of the outerreaction tube may be open, while the top end thereof may be closed,typically by a dome-shaped structure. The liner may be provided with aliner opening at both its top and lower end. Alternatively, the top endof the liner may be closed while there is a liner opening at the bottom.

The lower ends of both the outer reaction tube and the liner may besupported on a flange, which may define a central opening via which asubstrate boat holding a plurality of substrates may enter and exit thereaction chamber that is formed by the interior space of the liner. Thesubstrate boat may be supported on a thermally insulating pedestal,which in turn may be supported on a door plate that may serve to closeoff the central opening in the flange. The flange may further beprovided with a gas feed conduit that connects to a gas injectordisposed inside the liner, and a gas exhaust conduit via which a vacuumpump may be connected to a lower end of a gas passage that existsbetween an outer wall of the liner and an inner wall of the outerreaction tube.

In operation, a substrate boat with a plurality of substrates may beintroduced into the reaction chamber, which may then be evacuated.Subsequently, a process gas may be fed to the reaction chamber via thegas feed conduit and the gas injector. The process gas may flow into theinner space of the liner while contacting the substrates providedtherein. The process gas may exit the open top end of the liner andreach the closed top end of the outer reaction tube; it may reverse itsdirection and flow downwardly through the gas passage between the innerand outer reaction tubes, so as to be exhausted from the reactionchamber via the gas exhaust conduit by the vacuum pump.

An issue may be that the concentration of processing gas and reactionbyproducts may change during their way from the gas injector along thesubstrate boat. This may lead to processing non-uniformity betweensubstrates positioned on different positions in the substrate boat whichnon-uniformity may be unwanted. Further issues associated with verticalprocessing furnaces may be contamination of the reaction chamber withsmall deposit particles. A deposit particle that ends up on a substratebeing processed may render an integrated circuits to be manufacturedtherefrom inoperable.

A vertical furnace and a liner for use therein with improved propertiesmay therefore be desirable.

SUMMARY

This summary is provided to introduce a selection of concepts in asimplified form. These concepts are described in further detail in thedetailed description of example embodiments of the disclosure below.This summary is not intended to identify key features or essentialfeatures of the claimed subject matter, nor is it intended to be used tolimit the scope of the claimed subject matter.

In some embodiments a vertical furnace for processing a plurality ofsubstrates may be provided. The vertical furnace may comprise an outerreaction tube; and a liner constructed and arranged in the interior ofthe outer reaction tube. The liner may be substantially cylindrical anddelimited by a top end and a lower liner opening at a lower end anddefining an interior space within the liner for accommodating asubstrate boat with substrates. A gas passage may be defined between anouter wall of the liner and an inner wall of the reaction tube. Theliner may be provided with at least one gas exhaust hole on a side andextending from the interior space to the gas passage. At least one ofthe outer wall of the liner and the inner wall of the reaction tube maybe provided with at least one flow deflector that protrudes radiallyfrom the respective wall into the gas passage.

In some embodiments a liner constructed to extend in the interior of anouter reaction tube of a vertical furnace for processing a plurality ofsubstrates may be provided. The liner may be substantially cylindrical,having a central axis and delimited by a top end and a lower lineropening at a lower end and defining an interior space inside the linerfor accommodating a substrate boat with substrates. The liner may beprovided with at least one gas exhaust hole on a side and extending fromthe interior space to the outer side of the liner. The liner may beprovided with at least one flow deflector that protrudes radially froman outer wall of the liner.

For purposes of summarizing the invention and the advantages achievedover the prior art, certain objects and advantages of the invention havebeen described herein above. Of course, it is to be understood that notnecessarily all such objects or advantages may be achieved in accordancewith any particular embodiment of the invention. Thus, for example,those skilled in the art will recognize that the invention may beembodied or carried out in a manner that achieves or optimizes oneadvantage or group of advantages as taught or suggested herein withoutnecessarily achieving other objects or advantages as may be taught orsuggested herein.

All of these embodiments are intended to be within the scope of theinvention herein disclosed. These and other embodiments will becomereadily apparent to those skilled in the art from the following detaileddescription of certain embodiments having reference to the attachedfigures, the invention not being limited to any particular embodiment(s)disclosed.

BRIEF DESCRIPTION OF THE DRAWINGS

While the specification concludes with claims particularly pointing outand distinctly claiming what are regarded as embodiments of theinvention, the advantages of embodiments of the disclosure may be morereadily ascertained from the description of certain examples of theembodiments of the disclosure when read in conjunction with theaccompanying drawings, in which:

FIG. 1 is a schematic cross-sectional side view of an exemplaryembodiment of a vertical furnace according to an embodiment;

FIG. 2 depicts a schematic cross-sectional top view of a liner accordingto a further embodiment;

FIG. 3 depicts a schematic cross-sectional side view of the liner ofFIG. 2;

FIG. 4 depicts a side view of the liner of FIGS. 2 and 3; and,

FIG. 5 schematically illustrates an embodiment of a liner according to afurther embodiment.

DETAILED DESCRIPTION

Although certain embodiments and examples are disclosed below, it willbe understood by those in the art that the invention extends beyond thespecifically disclosed embodiments and/or uses of the invention andobvious modifications and equivalents thereof. Thus, it is intended thatthe scope of the invention disclosed should not be limited by theparticular disclosed embodiments described below. The illustrationspresented herein are not meant to be actual views of any particularmaterial, structure, or device, but are merely idealized representationsthat are used to describe embodiments of the disclosure.

As used herein, the term “substrate” may refer to any underlyingmaterial or materials that may be used, or upon which, a device, acircuit, or a film may be formed. The term “semiconductor devicestructure” may refer to any portion of a processed, or partiallyprocessed, semiconductor structure that is, includes, or defines atleast a portion of an active or passive component of a semiconductordevice to be formed on or in a semiconductor substrate. For example,semiconductor device structures may include, active and passivecomponents of integrated circuits, such as, for example, transistors,memory elements, transducers, capacitors, resistors, conductive lines,conductive vias, and conductive contact pads.

FIG. 1 schematically illustrates in a cross-sectional side view anexemplary vertical furnace or reactor 1 according to an embodiment. Thefurnace 1 is of a double tube type, and may include an outer reactiontube 30 which may be generally bell jar-shaped and a liner 40 which maybe open-ended and function as an inner reaction tube. The outer reactiontube 30 may be surrounded by heating means, such as a thermallyresistive heating coil 22 that is powered by an electrical power supply(not shown). The heating means may further be secured to a thermallyinsulating sleeve (not shown) that surrounds the outer reaction tube 30.Both the reaction tube 30 and the liner 40 may have a generally tubular,for example circular or polygonal, cross-sectional shape. An outerdiameter of the liner 40 may be smaller than an inner diameter of theouter reaction tube 30. Accordingly, the liner 40 may be at leastpartially disposed within the outer reaction tube 30, and extendsubstantially coaxially therewith around a common central axis L.

A gas passage 20 may be defined between an inner wall 32 of the outerreaction tube 30 and an outer wall 41 of the liner 40. In case thereaction tube 30 and the liner 40 have a similar cross-sectional shape,the gas passage 20 may have a substantially uniform width along itsaxial length. The (average) width of the gas passage may typically be onthe order of several centimeters, e.g. in the range of 1-5 centimeters.Both tube 30 and liner 40 may be made of quartz, silicon carbide,silicon or another suitable heat resistant material.

In the configuration shown in FIG. 1, the liner 40 may delimit areaction chamber 2 in which a substrate boat 26 is receivable. Both theouter reaction tube 30 and the liner 40 may be supported at their lowerend on a flange 8. The flange may be made of stainless steel. Thesubstrate boat 26 may enter and/or exit the reaction chamber 2 via acentral furnace opening 10 provided in the flange 8.

The substrate boat 26, which may include a plurality, e.g. between 10and 200, of slots for holding equally many substrates 27 e.g.semiconductor wafers, may be mounted on a pedestal 28, which may bemounted on a seal cap or door plate 12. The pedestal 28 may act as aheat shield for both the door plate 12 and the flange 8, and may reduceheat loss via the lower portion of the furnace 1. In some embodiments,the substrate boat 26 and the pedestal 28 may be rotatable by a motor(not shown).

To ensure that the reaction chamber 2 is sealed in a gas-tight manner,several seals such as elastomeric O-rings 14 may be employed in thelower part of the furnace 1, in particular between the outer reactiontube 30 and the flange 8, and between the flange 8 and the door plate12. Since the reliability of elastomeric O-rings and other seals maydiminish when subjected frequently or continuously to high temperatures,the lower part of the vertical furnace 1 may preferably be kept at alower temperature than that present in the central and upper parts ofthe reaction chamber 2.

The vertical furnace 1 may further include a gas injector 4. The gasinjector 4 may be disposed within reaction chamber 2 and include aplurality of gas injection holes 6 provided over the height or axiallength of the substrate boat 26. A gas feed conduit 18 may connect tothe gas injector 4, possibly via the flange 8, so as to enable theintroduction of process gases, e.g. precursor and/or purge gases, intothe reaction chamber 2 from the gas injection holes 6.

The vertical furnace may be used for a LPCVD process. In such a process,a precursor gas, for example tetraethylorthosilicate with the chemicalformula Si(OC₂H₅)₄ and the acronym “TEOS” may be used. TEOS may be usedas the source material for silicon oxide to be deposited on thesubstrates with a low pressure chemical vapor deposition process. Thisprocess may provide certain advantages in terms of uniformity or densityof the silicon oxide layer obtained. Alternatively, a silicon nitridelayer may be deposited with an LPCVD process with a different precursor.

The concentration of processing gas and reaction byproducts may changeafter leaving the gas injector 4. If the discharge or exhaust of processgas from the reaction chamber 2 is accomplished via the top opening ofthe inner reaction tub or liner 40, as described in U.S. Pat. No.8,398,773 incorporated by reference herein, the concentration ofprocessing gas and reaction byproducts may vary over the substrate boat26. This may lead to processing non-uniformity between substrates 27positioned on different positions in the substrate boat 26, whichnon-uniformity may be unwanted.

To minimize processing non-uniformity between substrates positioned ondifferent positions in the substrate boat gas exhaust holes 19 may beprovided in the liner 40 to discharge or exhaust gas from the reactionchamber 2. After passing the gas exhaust holes, the gas may turndownwardly through the gas passage 20 between the outer tube 30 and theliner 40, towards the gas exhaust conduit 16 connected to the vacuumpump 24. In FIG. 1 this gas exhaust path is indicated with referencenumeral 21.

The configuration of the gas injection holes 6 and the gas exhaust holes19 makes that process gas introduced into the reaction chamber 2 fromthe injection holes 6 of the gas injector 4 flows generally over thesubstrates through the reaction chamber towards the gas exhaust holes19. The path of the process gas and reaction byproducts in the reactionchamber may thereby be shortened compared to a situation where theprocess gas is exhausted from the top. This may minimize processingnon-uniformity between substrates positioned on different positions inthe substrate boat. Further the remaining non-uniformity may be in thehorizontal direction over the substrate which may be alleviated byrotation of the substrate boat 26.

While being exhausted, reactive gases may form a deposit as they flowthrough the relatively cold lower portion of the furnace 1, whichincludes the flange 8 and the gas exhaust conduit 16 (in the embodimentof FIG. 1 a part of the flange 8). In itself the deposition ofby-products adjacent the downstream end of the gas exhaust path 21 doesnot cause contamination of the reaction chamber 2. Under certainconditions, however, material deposited at the downstream end of the gasexhaust path 21 may be whirled up and be transported back, via the gaspassage 20, into the reaction chamber 2 by recirculating gas flows.

For instance, when after discharging one substrate boat 26 holdingprocessed substrates 27 from the reaction chamber 2 another substrateboat with a fresh batch of substrates 27 is being loaded into thereaction chamber 2, the reaction chamber 2 may be at atmosphericpressure and the vacuum pump 24 may be temporarily switched off. Theintroduction of the new, relatively cold substrate boat 26 with thelikewise cold unprocessed substrates 27 into the relatively warmreaction chamber 2 may cause significant temperature gradients withinthe reaction chamber, in particular between the outer reaction tube 30,the liner 40 and the substrate boat 26. These temperature gradients mayinduce pressure gradients and/or gas density gradients, which may, inturn, drive convective flows over the liner 40. These flows mayfacilitate particle transport from the downstream end of the exhaustpath 21, via the gas passage 20, the gas exhaust holes 19, back into thereactor chamber 2. This way, particles may end up on the substrates 27of the newly introduced substrate boat 26.

To prevent such back flow of deposits, the outer wall 41 of the liner 40and/or the inner wall 32 of the outer reaction tube 30 may be providedwith a flow deflector 50. The flow deflector may protrude from therespective wall into the gas passage 20, in a generally radial directionwith respect to the central axis L.

In the vertical furnace 1 of FIG. 1 both the outer reaction tube 30 andthe liner 40 may be provided with the flow deflector 50. The flowdeflector may be in the form of an annular baffle 52 that protrudesradially into the gas passage 20. The flow deflectors 50 may be providedat a point about halfway the axial length of the gas passage 20, andsufficiently close to each other to define a narrow Z-shaped gap betweenthemselves and the walls 32, 41 through which gas may pass. The baffles52 of the flow deflectors 50 may partially or completely encircle orsurround the liner 40, such that they necessarily obstruct the flow ofgas through the gas passage 20 in the direction of the central axis L,irrespective of the angular position of the gas flow relative to thecentral axis.

In order to warrant an efficient obstruction of a back flow, a flowdeflector may preferably protrude sufficiently far e.g. between 1 and 5cm into the gas passage 20. Precisely what is ‘sufficiently far’ maydepend in particular on the (local) width of the gas passage 20, i.e. onthe (local) distance between the inner wall 32 of the outer reactiontube 30 and the outer wall 41 of the liner 40. In general, the flowdeflector may preferably protrude radially from the wall on which it isprovided over a radial distance of at least 75% of a local width of thegas passage 20.

For example, in case the outer reaction tube 30 and the liner 40 definea cylinder jacket-shaped gas passage 20 with a uniform width of 25millimeters along the central axis L, the flow deflector 50 maypreferably extend a radial distance of at least 19 millimeters (i.e.0.75*25 mm) into the gas passage 20. In case the liner 40 is disposedslightly off-axis, e.g. by 5 mm, such that the width of the gas passage20 varies in the tangential direction between 20 and 30 mm, the distanceover which the flow deflector 50 protrudes into the gas passage 20 mayvary correspondingly, e.g. between 15 and 23 mm.

The liner 40 may be provided with an open tapered top end 54 at the topend of the liner. The open tapered top end 54 may have an openingsufficiently large, for example with a diameter of 310 to 350 mm, toallow the top of the substrate boat 26 to pass when the substrate boat26 moves in the inner space of the liner 40. The open tapered top end 54may be sufficiently small to prevent exhaust during processing from theopen tapered top. It may be preferred that the exhaust may beaccomplished through the exhaust hole 19 during processing.

The outer reaction tube 30 and liner 40 may normally be manufacturedindividually, and assembled at a later stage to form the double tubestructure of the furnace 1. To enable such assembly, during which theliner 40 is carefully moved into the outer reaction tube 30, at least afew millimeters of clearance between the two components may bedesirable. The clearance may preferably be at least 2 millimeters, andmore preferably be in the range of 2-8 millimeters. Accordingly, a flowdeflector may preferably protrude radially from the wall on which it isprovided over a radial distance of no more than a local width of the gaspassage 20 minus at least 2 millimeters, or over a radial distance of atleast the local width of the gas passage 20 minus 8 mm.

As will be illustrated with reference to FIGS. 2 to 5, a flow deflector50 may be composed of multiple parts, e.g. baffles, that may be providedat different axial positions, which parts together encircle the innertube 40. Multiple baffles, which may be provided on the walls 32, 41 ofthe outer reaction tube 30 and/or liners 40. Several embodiments of sucha flow deflector 50 will now be elucidated with reference to FIGS. 2 to5. It is noted in advance that in the embodiments depicted in FIGS. 2 to5, the baffles 52 of the flow deflector 50 are provided on the outerwall 41 of the liner 40, which liner is shown in isolation. One skilledin the art will appreciate, however, that similar patterns of bafflesmay alternatively, or in addition, also be provided on the inner wall 32of the outer reaction tube 30.

FIG. 2 depicts a cross-sectional top view of a liner 40 according to anembodiment. The liner 40 may be useable in a vertical furnace such asthe one of FIG. 1. The liner 40 may be provided with a bulge 55 whichmay be radially extending outward with respect to the central axis L ofthe liner. The bulge 55 may be extending parallel to the central axis Lof the liner to accommodate the gas injector 4 in the interior space ofthe liner 40. The bulge 55 may be extending in the gas passage 20 (seeFIG. 1) to accommodate the gas injector 4.

The liner 40 may be provided with a gas exhaust hole 19. It may beadvantageous to have the gas injector 4 configured opposite the gasexhaust hole 19 with respect to the central axis L of the liner 40. Thisconfiguration creates a flow over the full substrate if the process gasis provided to the gas injector 4 and removed from the inner space viathe gas exhaust hole 19. The bulge 55 in the liner 40 may therefore beconfigured opposite the gas exhaust hole 19 with respect to the centralaxis L.

The outer wall 41 of the liner 40 may be provided with a flow deflectorin the form of an annular baffle 52 which may protrude radially from theouter surface 41 around the liner 40. In the embodiment as shown in FIG.2 the baffle 52 may be hardly protruding at the position of the bulge 55at the outer surface 41 while the embodiment of FIG. 1 the baffle 52 isstill protruding substantially where the gas injector 4 is located atthe liner 40.

FIG. 3 depicts a cross-sectional side view on the liner 40 along theline 59 in FIG. 2. Shown is the substrate boat 26 including a pluralityof slots for holding a plurality of substrates 27 mounted on a pedestal28. The pedestal 28 may comprise a heat shield and may be rotatable by amotor (not shown). The outer wall 41 of the liner 40 may be providedwith a flow deflector in the form of an annular baffle 52 which mayprotrude radially from the outer surface 41.

The liner 40 may be provided with an open tapered top end 54 at the topend of the liner 40. The open tapered top end 54 may have an openingsufficiently large to allow the substrate boat 26 to pass when thesubstrate boat 26 moves in the inner space of the liner 40. When thesubstrate boat is moved into the inner space of the liner, the opentapered top end may be fully open since there is no substrate boat 26 inthe opening. The advantage is that any back flow through the gas passage20 likely will go through the opening at the top and not through the gasexhaust holes 19. The back flow will therefore pass all the flowdeflectors 52 and particles in the back flow may be obstructed beforereaching the substrates.

FIG. 4 depicts a side view on the liner 40 of FIGS. 2 and 3. Gas exhaustholes 19 may be provided in the liner 40 to discharge or exhaust gasfrom the inner space. The outer wall 41 of the liner 40 may be providedwith a flow deflector in the form of a plurality of annular baffles 52which may protrude radially from the outer surface 41.

The flow deflectors may comprise a hole flow deflector 56 which may bearranged within 10 mm from the gas exhaust hole 19. The hole flowdeflector 56 may be arranged near the lower side of the gas exhaust hole19. The hole flow deflector 56 may be provided with upstanding ridges 58directed parallel to the central axis L in a direction of the top end.The gas exhaust hole 19 may be slit shaped. The short side of the slitmay be directed in a direction parallel to the central axis L. Aparticle in the gas flow traveling along the outer wall 41 of the liner40 in the axial direction L may be obstructed by the flow deflectors,the hole flow deflectors, the ridges and/or the slit shape of the gasexhaust hole to reduce the risk of the particle entering the interiorspace. Multiple gas exhaust holes 19 in a vertical array may be providedin the liner. The multiple gas exhaust holes 19 in the liner 40 may havean increasing cross-section from bottom to top of the liner. Theincreasing cross-section may compensate for the increase of distance tothe vacuum pump 24 (in FIG. 1) so that for each gas exhaust hole 19 inthe array the volume of gas exhausted is substantially equal.

The liner 40 may be provided with an open tapered top end 54 at the topend of the liner 40. The open tapered top end 54 may have an openingsufficiently large to allow a substrate boat 26 to pass.

FIG. 5 schematically illustrates an embodiments of a liner 40 accordingto an embodiment. The embodiment features a flow deflector 50 comprisinga plurality of identical baffles 52 that protrude radially from, andextend substantially tangentially along, the outer wall 41 of the liner40 at different axial positions. Each of the baffles 52 may extendtangentially along the outer wall 41 of the liner 40 through an angle αof approximately 40 degrees relative to the central axis L. It iscontemplated, however, that in other embodiments the angle α of at leastsome of the baffles 52 may be smaller or larger than 40 degrees, e.g. bein the range of 30-90 degrees.

Furthermore, the baffles 52 may extend substantially perpendicular tothe outer wall 41. The baffles 52 may be disposed at a discrete numberof spaced apart axial positions, spread across the height of the liner40. For example, six baffles may be equidistantly spaced apart acrossthe height of the liner 40 as depicted in FIG. 5. Consequently, when theliner 40 is incorporated in a vertical furnace 1 similar to that shownin FIG. 1, the flow deflector 50 will be approximately uniformlydistributed over the length of the gas passage 20, at least such that itextends in all of three equally long axially extending portions of thegas passage 20 that together cover the total length thereof (e.g. in thedepicted orientation: a bottom portion, a middle portion and a topportion of the gas passage 20).

Each of the axial positions in the embodiment of FIG. 5 may feature anumber of tangentially spaced apart baffles 52. As depicted a series ofsix equidistantly tangentially spaced apart baffles 52 may be provided.The series of baffles 52 at different axial positions have beenrotationally offset relative to each other, and may partially overlapwhich each other, in such a way that, seen in the axial direction L, theflow deflector 50—i.e. all the baffles 52 considered inconjunction—encircle the liner 40 at least completely. In fact, they maybe considered to encircle the liner more than once.

Due to the fact that the flow deflector 50 is configured such that itencircles the liner 40 more than once, a gas flow traveling along theouter wall 41 of the liner 40 in the axial direction L may be obstructedseveral times by different baffles 52 of the flow deflector 50.Furthermore, because the flow deflector 50 is approximately uniformlydistributed over the axial length of the liner 40, there is noparticular axially extending portion of the outer wall 41 that is devoidof baffles 52 and that may for that reason facilitate the development ofrelatively strong back flows. Instead, the flow deflector 50 may beconsidered as somewhat of a maze made up of flow breaking/deflectingbaffles 52 that scatter developing, axially directed flows that might becapable of transporting deposit.

Gas exhaust holes 19 may be provided in the liner 40 to discharge orexhaust gas from the reaction chamber. The flow deflectors may comprisea hole flow deflector 56 which may be arranged within 10 mm from the gasexhaust hole 19 in the liner 40. The hole flow deflector may be arrangedtowards the lower side with respect to the gas exhaust hole 19. The gasexhaust hole may be slit shaped and the short side of the slit may bedirected in a direction parallel to the central axis L. Multiple gasexhaust holes in a vertical array may be provided in the liner. Themultiple gas exhaust holes 19 in the liner 40 may have an increasingcross-section from bottom to top along the liner.

According to an embodiment the flow deflector may include a number ofbaffles that extend helically along the outer wall of the liner aroundthe central axis L. From the perspective of back flow prevention, it maybe tempting to construct and employ a flow deflector with a relativelylarge number of baffles. However, a larger number of baffles may mean anincrease in flow resistance along the exhaust path, which in turn mayincrease the demands placed on the vacuum pump of a thermal processingfurnace. Numerical simulations have shown that the increase in flowresistance caused by the presence of a modest number of helicallyextending baffles may be relatively small and practically of no concernto most applications.

Although illustrative embodiments of the present invention have beendescribed above, in part with reference to the accompanying drawings, itis to be understood that the invention is not limited to theseembodiments. Variations to the disclosed embodiments can be understoodand effected by those skilled in the art in practicing the claimedinvention, from a study of the drawings, the disclosure, and theappended claims.

Reference throughout this specification to “one embodiment” or “anembodiment” means that a particular feature, structure or characteristicdescribed in connection with the embodiment is included in at least oneembodiment of the present invention. Thus, the appearances of thephrases “in one embodiment” or “in an embodiment” in various placesthroughout this specification are not necessarily all referring to thesame embodiment. Furthermore, it is noted that particular features,structures, or characteristics of one or more embodiments may becombined in any suitable manner to form new, not explicitly describedembodiments.

What is claimed is:
 1. A vertical furnace for processing a plurality ofsubstrates, comprising: an outer reaction tube; and a liner constructedand arranged to extend in the interior of the outer reaction tube andbeing substantially cylindrical and delimited by a top end and a lowerliner opening at a lower end and defining an interior space foraccommodating a substrate boat with substrates, wherein the linercomprises an open tapered top end at the top end of the liner; a gaspassage being defined between an outer wall of the liner and an innerwall of the reaction tube; the liner is provided with at least one gasexhaust hole on a side and extending from the interior space to the gaspassage; wherein at least one of the outer wall of the liner and theinner wall of the reaction tube is provided with at least one flowdeflector that protrudes radially from the respective wall into the gaspassage.
 2. The vertical furnace according to claim 1, wherein the flowdeflector at least partially encircles the liner, such that a flow ofgas through the gas passage in the direction of the central axis isobstructed at least once by said flow deflector.
 3. The vertical furnaceaccording to claim 1, wherein the flow deflector protrudes radially fromthe respective wall over a distance of at least 75% of a local width ofthe gas passage.
 4. The vertical furnace according to claim 1, whereinthe flow deflector extends substantially tangentially over therespective walls.
 5. The vertical furnace according to claim 1, whereinthe flow deflector comprises a hole flow deflector which is arrangedwithin 10 mm from the gas exhaust hole in the liner.
 6. The verticalfurnace according to claim 5, wherein the hole flow deflector isarranged towards the lower side with respect to the gas exhaust hole inthe liner.
 7. The vertical furnace according to claim 5, wherein thehole flow deflector is provided with upstanding ridges directed parallelto a central axis of the reaction tube in a direction toward the topend.
 8. The vertical furnace according to claim 1, wherein the gasexhaust hole is slit shaped and a short side of the slit is directed ina direction parallel to a central axis of the reaction tube.
 9. Thevertical furnace according to claim 1, wherein multiple gas exhaustholes in a vertical array are provided in the liner.
 10. The verticalfurnace according to claim 1, wherein the vertical furnace is providedwith an injector extending parallel to a central axis in the inner spaceof the liner to provide a process gas in the inner space.
 11. Thevertical furnace according to claim 10, wherein the liner is providedwith a bulge extending in the gas passage parallel to the central axisto accommodate the injector in the interior space.
 12. The verticalfurnace according to claim 10, wherein the injector is provided oppositethe gas exhaust hole with respect to the central axis.
 13. The verticalfurnace according to claim 1, wherein multiple flow deflectors create ameandering flow path in the gas passage and the flow deflector includesa baffle.
 14. The vertical furnace according to claim 1, wherein thefurnace is provided with a vacuum pump constructed and arranged toremove gasses from the inner space via the gas exhaust hole in the linerand the gas passage.
 15. The vertical furnace according to claim 1,wherein the vertical furnace is provided with an injector extendingparallel to the central axis in the inner space of the liner andconnected to a process gas source.
 16. The vertical furnace according toclaim 1, wherein the process gas source comprises a precursor gasevaporator constructed and arranged to evaporate Tetraethylorthosilicate(TEOS).
 17. A liner constructed to extend in the interior of an outerreaction tube of a vertical furnace for processing a plurality ofsubstrates, the liner being substantially cylindrical, having a centralaxis and delimited by a top end and a lower liner opening at a lower endand defining an interior space inside the liner for accommodating asubstrate boat with substrates, wherein the top end of the linercomprises a top liner opening which is tapered; the liner being providedwith at least one gas exhaust hole on a side and extending from theinterior space to the outer side of the liner; the liner being providedwith at least one flow deflector that protrudes radially from an outerwall of the liner.
 18. The liner according to claim 17, wherein the flowdeflector protrudes radially from the outer wall of the liner over adistance between 1 and 5 cm.
 19. The liner according to claim 17,wherein the flow deflector at least partially encircles the liner. 20.The liner according to claim 17, wherein the flow deflector extendssubstantially tangentially over the outer wall of the liner.
 21. Theliner according to claim 17, wherein the flow deflector comprises a holeflow deflector which is arranged within 10 mm from the gas exhaust holein the liner.
 22. The liner according to claim 21, wherein the hole flowdeflector is arranged towards the lower end of the liner with respect tothe gas exhaust hole in the liner.
 23. The liner according to claim 21,wherein the hole flow deflector is provided with upstanding ridgesdirected parallel to the central axis in a direction toward the top end.24. The liner according to claim 17, wherein the gas exhaust hole isslit shaped and a short side of the slit is directed in a directionparallel to the central axis.
 25. The liner according to claim 17,wherein multiple gas exhaust holes in a substantially vertical arrayparallel to the central axis are provided in the liner.
 26. The lineraccording to claim 17, wherein the liner is provided with a bulgeextending parallel to the central axis to accommodate an injector in theinterior space.
 27. The liner according to claim 26, wherein the bulgeis provided opposite the gas exhaust hole with respect to the centralaxis.
 28. The liner according to claim 17, wherein multiple flowdeflectors create a meandering flow path over the outer wall of theliner and the flow deflector includes a baffle.